One of the more difficult problems associated with any borehole is to communicate measured data between one or more locations down a borehole and the surface, or between downhole locations themselves. For example, in the oil and gas industry it is desirable to communicate data generated downhole to the surface during operations such as drilling, perforating, fracturing, and drill stem or well testing; and during production operations such as reservoir evaluation testing, pressure and temperature monitoring. Communication is also desired to transmit intelligence from the surface to downhole tools or instruments to effect, control or modify operations or parameters.
Accurate and reliable downhole communication is particularly important when complex data comprising a set of measurements or instructions is to be communicated, i.e., when more than a single measurement or a simple trigger signal has to be communicated. For the transmission of complex data it is often desirable to communicate encoded analog or digital signals. These transmissions can be performed through direct wire connection between the surface and the downhole location(s) or through wireless communications techniques such as electromagnetic waves, pressure or fluid pulses, and acoustic communication.
A tubing is composed of many pipes linked together by connections. There are few nominal sizes for the outside diameter (for example 2⅞ inches, 3.5 inches or 4.5 inches). The outside diameter has a rather large tolerance which is defined by norms edited by the American Petroleum Institute. The connection between pipes, which may be called a “coupling”, comprises a thread, and a very large variety of connections exist on the present market. Most of the time, the coupling outside diameters are larger than a diameter of the pipe.
When a device, such as a sensor (temperature, pressure) or a transmitter (for example acoustic transmitter) must be secured on the pipe, such device can either be installed in a carrier (also called a mandrel) placed between two pieces of pipe (see for example, U.S. Pat. No. 7,339,494) or it can be clamped directly along the outside diameter of the pipe, using one or several mechanical collars called “clamps”. Usually, the prior art clamps are made of at least two parts which are secured together so that they can be directly installed on the tubing, without engaging the connections.
However, a tool secured outside of the tubing can be exposed to large axial loads and shock when the pipe is moving inside an open hole (whose rugged surface can generate a high friction force when dragging), or when the tool engages a liner. The liner, for example, may be a casing of smaller size located in a lower part of a well. Therefore, the liner forms an abrupt change in diameter with the upper casing. When the tool is an acoustic modem, such acoustic modem has a transceiver assembly which vibrates to introduce axial stress waves into the tubing. In this instance, the acoustic modem should be securely connected to the tubing to maximize the signal transferred from the acoustic modem into the tubing.
As discussed above, clamps are often used for attaching downhole communications tools and/or wires to a downhole pipe. Clamps are well known in the art and take the form of hinged friction collars, hinged collars with set screws, and hinged collars with dogs. See for example, U.S. Pat. No. 6,957,704.
Other means for attaching downhole tools to a section of pipe include drill stem testing (DST) gauge carriers. These DST gauge carriers (DGA) are used to secure downhole pressure and temperature measuring gauges to sections of pipe to measure temperature and pressure conditions within the well bore. A DGA can be attached to a packer, as disclosed in U.S. Pat. No. 4,628,995, along with a packer through the tubing. As disclosed in U.S. Pat. No. 4,593,771, a DGA can be integrated into a section of pipe using either a single location of attachment for a downhole pressure and temperature gauge or multiple attachment points for securing multiple downhole pressure and temperature gauges without interconnecting the multiple gauges to each other. An advantage to mounting the pressure and temperature gauges to the exterior of a section of pipe through a clamp mechanism or with the DGA integrated into the exterior of the section of pipe is that pressure and temperature measurements can be obtained without substantial pressure drop across the measuring sub or preventing flow through the section of pipe.
When a device, such as a sensor (temperature, pressure) or a transmitter (for example acoustic transmitter) must be secured on the pipe, such device usually requires electric wires to be connected to the tool so that it can transmit or receive information to or from the surface or to or from another tool. The traditional way, widely used in the oil and gas industry is to link the devices by electric wires protected by rubber boots, as in U.S. Pat. Nos. 5,344,377, 5,493,626, and 5,667,009. The boots ensure an electrical insulation against the downhole fluid under high pressure and can protect the electric connectors during the installation process. The electric contact to link the wire to the internal components of the device must create the pressure barrier. This component, a feed-through connector, is usually quite expensive. Further, boot assemblies can be unreliable for long term use in the downhole environment, because of the difficulty in ensuring perfect sealing between the rubber boot and the plastic insulation on the wires. In addition, the rubber can be slightly permeable, allowing gas and oil to slowly migrate inside the rubber. This migration reduces the dielectric properties of the rubber. When moisture is allowed to penetrate inside the boot, the moisture decreases the insulation and jeopardizes the reliability of the system.
Despite the efforts of the prior art, there exists a need for an electrical connection, such as a junction box, to create a more reliable seal around electrical connections of downhole tools. In addition, there is a need to connect multiple downhole tools through a junction box which maintains a reliable seal around the electrical connections. It is therefore desirable to provide an improved junction box or electrical connection seal assembly with better sealing capabilities for downhole tools. It is to such a junction box that the present disclosure is directed.